Measuring Earthquakes

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Vocabulary

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focus-rock under the surface breaks,creating an earthquake
epicenter-point directly above the surface
seismic waves-carries energy released in an earthquake
P waves-waves that squeeze and stretch the Earth
S waves-waves that move from side-to-side as well as up-and-down
Surface waves-waves that move like ocean waves
seismograph-records ground movements caused by seismic waves
magnitude-measurement of Earthquake strength
Mercalli scale-rates earthquake on strength
Richter scale-rating of how big a seismic wave is
moment magnetude scale-rates total energy of an earthquake

Outline

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seismic waves

• energy is greatest at the epicenter
• primary waves(P waves)
  • squeezes and stretches the ground
    • causes buildings to do the same thing as the ground
• Secondary Waves (S waves)
  • comes after P waves
    • moves from side-to-side as well as up-to-down
      • shakes buildings viciously
• Surface Waves
  • makes more severe earthquakes
    • rolls like ocean waves
      • P waves come first, then S waves, then Surface Waves

Detecting Seismic Waves

• seismograph records ground movements

Measuring Earthquakes

• Magnitude is the measurement of Earthquakes
• The Mercalli Scale
  • developed in early 20th century
    • rates Earthquakes on Strength
• The Richter Scale
  • developed in 1930s
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  • rates how big a seismic wave is
• The Moment Magnitude Scale
  • rates the energy released during an Earthquake

Locating the Epicenter

• Geologists use seismic waves to locate the Earthquake's epicenter
  • the farther away the Earthquake,the more time of the arrival of the P and S waves

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